Self-healing rubber composition and tire

ABSTRACT

The present invention is directed to a self-healing rubber composition comprising a functionalized elastomer comprising: a polymeric backbone chain derived from a monomer comprising at least one conjugated diene monomer and optionally at least one vinyl aromatic monomer; and a functional group bonded to the backbone chain, the functional group comprising a multidentate ligand capable of complexing with a metal ion; and a partitioned metal ion. 
     The invention is further directed to a pneumatic tire comprising the self-healing rubber composition.

BACKGROUND

Tires are subjected to one of the harshest environments experienced byany consumer product. In addition to being stretched millions of timesas they roll through their life, tires are exposed to acid rain, brakedust, harsh chemicals and direct sunlight, as well as summer's heat andwinter's cold. In some cases, tires may develop cracks in the tirerubber in these environments.

Poor tire maintenance practices (or other conditions) can increase thelikelihood of developing cracks. For example, driving on a tire that isflat or a run flat tire under run flat conditions, or one that isunderinflated or overloaded causes excessive stretching of the rubbercompound, and may result in (or exacerbate) cracks.

In addition, simple exposure of tires to the elements can eventuallycause rubber to lose some of its elasticity and allow surface crackingto appear. These cracks typically develop in the sidewalls or at thebase of the tread grooves. Cracking can be accelerated by too muchexposure to heat, vehicle exhaust, ozone and sunlight. Additionally,some sidewall cracking has been linked to abrasion from parking againsta curb, or the excessive use of tire cleaners/dressings thatinadvertently remove some of the tire's anti-oxidants and anti-ozonantsprotection during every cleaning procedure. Depending on their severity,they may be cosmetic in nature if they don't extend past the rubber'souter surface, or may be a reason to replace the tire if they reach deepinto the rubber.

The repeated stretching of the rubber compound actually helps resistcracks forming. The tires used on vehicles that are driven infrequently,or accumulate low annual mileage are more likely to experience crackingbecause long periods of parking or storage interrupt “working” therubber. In addition to being an annoyance to show car owners, thiscondition often frustrates motor home and recreational vehicle ownerswho only take occasional trips and cannot park their vehicle in a garageor shaded area. Using tire covers at least minimizes direct exposure tosunlight.

It would thus be desirable to provide a tire with an ability to repairits own cracks by repairing damage to the polymeric structure of thetire, thereby maintaining strength and durability, and extending thelife of the tire.

SUMMARY

The present invention is directed to a self-healing rubber compositioncomprising a functionalized elastomer comprising: a polymeric backbonechain derived from a monomer comprising at least one conjugated dienemonomer and optionally at least one vinyl aromatic monomer; and afunctional group bonded to the backbone chain, the functional groupcomprising a multidentate ligand capable of complexing with a metal ion;and a partitioned metal ion.

The invention is further directed to a pneumatic tire comprising theself-healing rubber composition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic representation of a coordination complexbetween a metal ion and a functionalized elastomer.

FIG. 2 shows a fragmentary cross-sectional view of a runflat tireshowing its tread and carcass with one ply and one insert axially inwardof the ply in the sidewall region of the tire as an embodiment of theinvention.

FIG. 3 shows an enlarged view of the in-circle portion of FIG. 2showing, in cross-section, the encapsulated metal ion in accordance withan embodiment of the present invention.

FIG. 4 shows the ¹H-NMR spectrum of a styrene-butadiene elastomer.

FIG. 5 shows the UV-vis spectrum of a styrene-butadiene elastomer beforeand after the reaction with 2-mercaptonaphtalene and the spectrum of thepure thiol.

FIG. 6 shows the UV-vis spectrum of a styrene-butadiene elastomer beforeand after the reaction with 2-mercaptonaphtalene and the spectrum of thepure thiol.

FIG. 7 shows the ¹H-NMR spectrum of a styrene-butadiene elastomer beforeand after reaction with a thiol in the presence of different initiators.

FIG. 8 shows a GPC-measurement for a styrene-butadiene elastomer, andthe elastomer functionalized with a thiol in the presence of differentinitiators.

FIG. 9 shows an ¹H-NMR of an unfunctionalized styrene-butadieneelastomer compared to the elastomer functionalized with a terpyridineligand.

FIG. 10 shows a GPC graph for an unfunctionalized styrene-butadieneelastomer compared to the elastomer functionalized with a terpyridineligand.

FIG. 11 shows an ¹H-NMR of an unfunctionalized styrene-butadieneelastomer compared to the elastomer functionalized with a terpyridineligand.

FIG. 12 a synthesis scheme for synthesis of a terpyridine ligand.

FIG. 13 shows an ¹H-NMR of a terpyridine ligand compared to astyrene-butadiene elastomer functionalized with the terpyridine ligand.

FIG. 14 shows UV-vis spectra for a rubber cement/iron salt mixture andfor rubber cement.

FIG. 15 shows UV-vis spectra for a rubber cement/ruthenium salt mixtureand for a rubber cement.

DETAILED DESCRIPTION

There is disclosed a self-healing rubber composition comprising afunctionalized elastomer comprising: a polymeric backbone chain derivedfrom a monomer comprising at least one conjugated diene monomer andoptionally at least one vinyl aromatic monomer; and a functional groupbonded to the backbone chain, the functional group comprising amultidentate ligand capable of complexing with a metal ion; and apartitioned metal ion.

There is further disclosed a pneumatic tire comprising the self-healingrubber composition.

In one embodiment, the functionalized elastomer has the structure I

XY—Z]_(n)  (I)

where X is a polymer derived from a monomer comprising at least oneconjugated diene monomer and optionally at least one vinyl aromaticmonomer; Z is a functional group comprising a multidentate ligandcapable of complexing with a metal ion; Y is a divalent group bonded toboth X and Z; and n is the number of Y—Z] groups bonded to X.

In one embodiment, the polymer X is a diene based elastomer comprisingat least one carbon-carbon double bond. The phrases “rubber or elastomercontaining olefinic unsaturation” or “diene based elastomer” as usedherein are equivalent and are intended to include both natural rubberand its various raw and reclaim forms as well as various syntheticrubbers. In the description of this invention, the terms “rubber” and“elastomer” may be used interchangeably, unless otherwise prescribed.The terms “rubber composition,” “compounded rubber” and “rubbercompound” are used interchangeably to refer to rubber which has beenblended or mixed with various ingredients and materials and such termsare well known to those having skill in the rubber mixing or rubbercompounding art. Representative synthetic rubbers are thehomopolymerization products of butadiene and its homologues andderivatives, for example, methylbutadiene (i.e., isoprene),dimethylbutadiene and pentadiene as well as copolymers such as thoseformed from butadiene or its homologues or derivatives with otherunsaturated monomers. Among the latter are acetylenes, for example,vinyl acetylene; olefins, for example, isobutylene, which copolymerizeswith isoprene to form butyl rubber; vinyl compounds, for example,acrylic acid, acrylonitrile (which polymerize with butadiene to formNBR), methacrylic acid and styrene, the latter compound polymerizingwith butadiene to form SBR, as well as vinyl esters and variousunsaturated aldehydes, ketones and ethers, e.g., acrolein, methylisopropenyl ketone and vinylethyl ether. Specific examples of syntheticrubbers include neoprene (polychloroprene), polybutadiene (includingcis-1,4-polybutadiene), polyisoprene (including cis-1,4-polyisoprene),butyl rubber, halobutyl rubber such as chlorobutyl rubber or bromobutylrubber, styrene/isoprene/butadiene rubber, copolymers of 1,3-butadieneor isoprene with monomers such as styrene, acrylonitrile and methylmethacrylate, as well as ethylene/propylene terpolymers, also known asethylene/propylene/diene monomer (EPDM), and in particular,ethylene/propylene/dicyclopentadiene terpolymers. Additional examples ofrubbers which may be used include alkoxy-silyl end functionalizedsolution polymerized polymers (SBR, PBR, IBR and SIBR), silicon-coupledand tin-coupled star-branched polymers. The preferred rubber orelastomers for use as polymer X are polyisoprene (natural or synthetic),polybutadiene and SBR.

In one embodiment, polymer X may be an emulsion polymerization derivedstyrene/butadiene (E-SBR) might be used having a relatively conventionalstyrene content of about 20 to about 28 percent bound styrene or, forsome applications, an E-SBR having a medium to relatively high boundstyrene content, namely, a bound styrene content of about 30 to about 45percent.

By emulsion polymerization prepared E-SBR, it is meant that styrene and1,3-butadiene are copolymerized as an aqueous emulsion. Such are wellknown to those skilled in such art. The bound styrene content can vary,for example, from about 5 to about 50 percent. In one aspect, the E-SBRmay also contain acrylonitrile to form a terpolymer rubber, as E-SBAR,in amounts, for example, of about 2 to about 30 weight percent boundacrylonitrile in the terpolymer.

Emulsion polymerization prepared styrene/butadiene/acrylonitrilecopolymer rubbers containing about 2 to about 40 weight percent boundacrylonitrile in the copolymer are also contemplated as diene basedrubbers for use as polymer X in this invention.

The solution polymerization prepared SBR (S-SBR) suitable for use aspolymer X typically has a bound styrene content in a range of about 5 toabout 50, preferably about 9 to about 36, percent. The S-SBR can beconveniently prepared, for example, by organo lithium catalyzation inthe presence of an organic hydrocarbon solvent.

In one embodiment, cis 1,4-polybutadiene rubber (BR) may be used aspolymer X. Such BR can be prepared, for example, by organic solutionpolymerization of 1,3-butadiene. The BR may be convenientlycharacterized, for example, by having at least a 90 percent cis1,4-content.

The term “phr” as used herein, and according to conventional practice,refers to “parts by weight of a respective material per 100 parts byweight of rubber, or elastomer.”

In one embodiment, the functional group Z comprising a multidentateligand capable of complexing with a metal ion, includes but is notlimited to substituted or unsubstituted bipyridinyl groups, substitutedor unsubstituted terpyridinyl groups, substituted or unsubstitutedphenanthrolinyl groups, and substituted or unsubstituted pyrazinylgroups, and the like.

In one embodiment, the functional group Z comprising a multidentateligand capable of complexing with a metal ion is selected from the groupconsisting of substituted or unsubstituted bipyridinyl groups,substituted or unsubstituted terpyridinyl group, substituted orunsubstituted phenanthrolinyl group, or substituted or unsubstitutedpyrazinyl group.

In one embodiment, the functional group Z comprising a multidentateligand capable of complexing with a metal ion is a substituted orunsubstituted terpyridinyl group of formula II, or substituted orunsubstituted bipyridinyl group of formula III or IV

where R¹ forms the linkage from Z to Y in formula I and R¹ is a covalentbond, C2 to C8 linear alkylene, arylene, alkyl substituted arylene, arylsubstituted alkylene, thioalkylene, or thioarylene, and R² areindependently selected from the group consisting of hydrogen, C1 to C6linear alkyl, and C2 to C6 branched alkyl.

In one embodiment, the functional group Z comprising a multidentateligand is a substituted or unsubstituted 2,2′;6′,2″-terpyridinyl group.

In one embodiment, the functional group Z comprising a multidentateligand is a substituted or unsubstituted 2,2′-bipyridinyl group.

In one embodiment, the Y—Z] group is selected from the group consistingof 6-(2,2′;6′,2″-terpyridin-4′-ylsulfanyl)hexyl-1-sulfanyl,2,2′;6′,2″-terpyridin-4′-ylsulfanyl, and4-(2,2′;6′,2″-terpyridin-4′-yl)phenylmethylsulfanyl.

Y is a divalent group bonded to both X and Z. In one embodiment, Y issulfur or oxygen. In one embodiment, Y is sulfur.

The number n of Y—Z] groups bonded to X ranges from about 2 to about 30in a given copolymer molecule.

By “capable of complexing with a metal ion,” it is meant that as part ofthe functionalized elastomer of formula I, the functional group Z mayform a complex structure with a metal ion; such a metal ion may bepresent for example by addition of a metal salt during mixing of thefunctionalized elastomer in a rubber composition. Suitable metal ionsinclude those known to complex with ligands, including but not limitedto zinc ions, copper ions, iron ions, ruthenium ions, and the like. Thecomplexation of the functional group Z with a metal ion may exist as acomplex between a single functional group Z and the metal ion, or as acoordination complex between 2 or more functional groups Z and a metalion. FIG. 1 shows schematically such a coordination complex between anelastomer (1) shown as a wavy line functionalized through a sulfurlinkage (2) with a terpyridine group (3) as the ligand. The addition ofa metal ion M (4) is shown to form a coordination complex (5) betweenthe metal ion M (4) and two of the ligand groups (3) of thefunctionalized elastomer.

The functionalized elastomer may be produced by various methods. In oneembodiment, the functionalized elastomer may be produced byfunctionalizing the polymer X with functional group Z comprising amultidentate ligand capable of complexing with a metal ion. A convenientway for the functionalization of a variety of elastomers is thethiol-ene reaction during which alkene moieties being present in theelastomers are transformed into thioethers by reaction with thiols. Thisreaction proceeds preferably with vinyl groups as they are present instyrene-butadiene rubbers, butadiene rubbers, and polyisoprene rubbers.In order to allow the functionalization of the elastomers, the Y—Z]grouping, where Y is sulfur, may be linked to the elastomer X throughreaction of the thiol HS-Z with vinyl groups of the elastomer X to forma thioether of formula I, where Y is sulfur. Further details of thethiol-ene reaction as it relates to elastomers may be found by referenceto U.S. Pat. Nos. 6,365,668 and 7,847,019, both fully incorporated byreference herein.

One step of the method to produce the functionalized elastomer is toobtain as a first polymer X, an elastomer comprising at least onecarbon-carbon double bond.

A second step of the method is obtaining a functionalizing agentincluding a functional group Z comprising a multidentate ligand capableof complexing with a metal ion, and a functional group Y capable ofreacting with the carbon-carbon double bond of the first polymer.

A third step of the method is reacting the first polymer X with thefunctionalizing agent to form the functionalized elastomer. Duringreacting of the functionalizing agent with the first polymer, thefunctional group Z is linked to the first polymer through reaction ofthe functional group Y with the unsaturated carbon-carbon bond of thefirst polymer.

In one embodiment, the functionalizing agent is reacted with the firstpolymer in a suitable solvent in the presence of a free-radicalinitiator via a thiol-ene reaction as is known in the art, see forexample Macromolecules 2008, 41, 9946-9947. In one embodiment, thefree-radical initiator is selected from the group consisting of2,4,6-Trimethylbenzoyldiphenylphosphine oxide and azobisisobutyonitrile(AIBN).

In addition to the functionalized elastomer, the self-healing rubbercomposition includes a partitioned metal ion. By partitioned, it ismeant that in the self-healing rubber composition, the metal ion isisolated from the functionalized elastomer by a partition. The partitionmay be disrupted by some stressor, so that the metal ion is exposed tothe functionalized elastomer leading to the previously describedcomplexation of the functionalized elastomer and metal ion. In oneembodiment, the stressor is a mechanical stress, such as imparted by thepropagation of a crack in a tire component made from the self-healingrubber composition. In this embodiment, when a crack meets the partitionthe stress causing the crack propagation is transferred to thepartition, thus breaking the partition and released the metal ion. Insuch an embodiment, the partition is a mechanically disruptiblepartition.

In one embodiment, the partitioned metal ion is an encapsulated metalion. The disposition of an encapsulated metal ion is illustrated in theembodiment illustrated in FIGS. 2 and 3.

FIG. 2 shows a fragmentary cross-section of a runflat tire 1, its tread2, bead portion 3, sidewall or sidewall region 4, inextensible wire beadcore 5, rubber chafer 6, rubber toeguard 7, rubber compositioninnerliner 8, belt structure 9 underlying a portion of the tread 2,carcass ply 10, carcass ply turnup 11, rubbery sidewall insert 12 andapex 13. The sidewall insert 12 may extend from each bead regionradially to the edge of the tread, usually to just beneath thereinforcing belt structures 9.

An encapsulated metal ion 18, as shown in FIG. 3, is provided dispersedin sidewall insert 12 of the runflat tire 1. The encapsulated metal ion18 includes a metal ion 20 encapsulated by a coating material defining amicrocapsule 22. The rubbery sidewall insert 12, containing theencapsulated metal ion 18, generally can be formulated by means andmethods known to those having ordinary skill in the art.

The coating material of the microcapsule can be selected from amultitude of materials or mixtures thereof. For example, the coating mayinclude waxes such as paraffins, resins such as phenol formaldehyde orurea formaldehyde, carbon pitches, thermoplastic elastomers such asKraton™ and thermoplastics such as syndiotactic polybutadiene,polyethylene (PE), polyethylene oxide, polyvinyl acetate, ethylene-vinylacetate copolymers, polyvinyl alcohols (PVA), polyacrylic acid andderivatives, polycarbonates, polymethylmethacrylate (PMMA),polyorthoester, polyvinylpyrrolidone, or polypropylene (PP). In oneembodiment, the coating material is polypropylene. In anotherembodiment, the coating material is paraffin. In yet another embodiment,the coating material is urea formaldehyde.

Since the encapsulated metal ion is processed with rubbery polymers, asfurther discussed below, to ultimately provide a rubber compound, e.g.,suitable for use in tire 1, the coating material selected must be ableto withstand the processing temperatures. Such processing can includemixing, calendaring, extrusion, and curing (or vulcanization) steps, forexample. Of the processing steps, vulcanization includes the highesttemperature encountered by the coating material of the encapsulatedmetal ion, which may be from about 120° C. to about 180° C. depending onthe characteristics of the rubber composition, for example as used intire 1.

To that end, the coating material of the microcapsule 22 is chosen so asto be thermally stable at the temperatures it encounters duringprocessing of the rubber compound, which includes curing. Accordingly,the coating material for the microcapsule 22 is selected to both preventrelease of the metal ion 20 during the processing steps, such as canoccur through melting or softening of the coating material, and torelease the metal ion 20, such as by rupture due to mechanical stress ofa propagating crack in the rubber. This release can allow the metal ion20 to interact with the functionalized elastomer, by complexing with thesurrounding rubber. In this way, the propagation of the crack may behalted and the crack may be at least partially closed by thecomplexation of the metal ion with the functionalized elastomer, therebyself-healing the crack.

The coating thickness of the microcapsule also must provide enoughdurability for the encapsulated metal ion to withstand the rigors ofprocessing, such as mixing, but allow for rupture during, for example,the mechanical stress of a propagating crack. As such, in one example,the coating thickness is about 18 nm to about 6000 nm thick. Also, thediameter of the microcapsules can vary widely but generally may be fromabout 1 micron to about 2000 microns. In one embodiment, the diameter isfrom about 10 micron to about 150 microns.

Microencapsulation techniques are known to those having ordinary skillin the art. To that end, the encapsulated metal ion can be prepared in avariety of ways. One feature of the processes is that microcapsules areformed completely encasing metal ion to provide microcapsules of thetype and size described above. In one example, the microcapsule isformed of a synthetic resin material, and may be produced by well-knownpolymerization methods, such as interfacial polymerization, in-situpolymerization or the like. In another example, the encapsulated metalion may be prepared by allowing a mixture, which contains metal ion,molten coating material, and optionally other auxiliaries such assurfactants or dispersants, to flow in a cooling column onto a rapidlyrotating device such as a rotary table and migrate to the outsidebecause of the high centrifugal force. Because the diameter is greaterat the edge, the particles are separated and the formation ofagglomerates avoided. After being flung off from the edge of therotating device, the particles, or encapsulated metal ion, fly away tothe outside individually and cool in the process, as a result of whichthe coating solidifies.

Other processes, such as spray-drying, fluidized-bed coating, emulsionor suspension processes and precipitation also come into considerationfor the preparation of the encapsulated metal ion.

In one embodiment, the encapsulated metal ion may be treated on itsexterior surface with an adhesive to promote adhesion between theencapsulating material and the surrounding rubber. In one embodiment,the adhesive is a resorcinol-formaldehyde-latex (RFL) type adhesive asis known in the tire compounding art.

Upon release of metal ion from the encapsulating partition, as forexample during the mechanical stress of a propagating crack in the tirerubber, the metal ion is released from the microcapsule and exposed tothe surrounding rubber composition, including the functionalizedelastomer. While not wishing to be bound by any theory, when in thepresence of the functionalized elastomer, the metal ion may complex withthe functionalized elastomer in a manner similar to that illustrated inFIG. 1 and described earlier herein. In FIG. 1, the metal ion M isillustrated as freely associated with the functionalized elastomer, sucha through addition of a metal salt to the rubber composition.

In another embodiment, the partitioned metal ion is in the form of acomplex with a polymeric ligand. Suitable polymeric ligands includethose polymeric ligands that under predetermined conditions have weakercomplexation with the metal ions than the functionalized elastomer doeswith the metal ion. For example, a suitable polymeric ligand mayselectively complex with the metal ion at relatively low temperature,but at higher predetermined temperature such as that in localizedpropagating crack. In one embodiment, the polymeric ligand is apolyamine or polycarboxylic acid. In one embodiment, the polymericligand is poly(ethylene imine) or polyacrylic acid. The amount ofpolymeric ligand required to complex with the metal ion and form apartitioned metal ion is readily determinable by one skilled in the artwithout undue experimentation.

The metal ion is generally added in an amount sufficient to complex withthe functionalized elastomer; depending on the amount of functionalizedelastomer present in the rubber composition and the number of ligandgroups in an elastomer molecule, the amount of metal ion required can beeasily determined by one skilled in the art. Amounts of metal ion inexcess of, or less than, the stoichiometric amount of metal ion may beused, depending on the desired effect.

In one embodiment, the metal ion includes divalent copper, divalentiron, divalent cobalt, divalent nickel, and divalent ruthenium, i.e.,Cu²⁺, Fe²⁺, Co²⁺, Ni²⁺, Zn²⁺ and Ru²⁺.

In one embodiment, the metal ion is added to the rubber composition as ametal salt. In one embodiment, the metal ion is added to the rubbercomposition as a metal salt including FeSO₄.7H₂O, FeCl₂, NiCl₂, RuCl₃,cobalt stearate, zinc stearate, and the like.

The self-healing rubber composition may optionally include, in additionto the functionalized elastomer and the encapsulated metal ion, one ormore rubbers or elastomers containing olefinic unsaturation. The phrases“rubber or elastomer containing olefinic unsaturation” or “diene basedelastomer” are intended to include both natural rubber and its variousraw and reclaim forms as well as various synthetic rubbers. In thedescription of this invention, the terms “rubber” and “elastomer” may beused interchangeably, unless otherwise prescribed. The terms “rubbercomposition,” “compounded rubber” and “rubber compound” are usedinterchangeably to refer to rubber which has been blended or mixed withvarious ingredients and materials and such terms are well known to thosehaving skill in the rubber mixing or rubber compounding art.Representative synthetic polymers are the homopolymerization products ofbutadiene and its homologues and derivatives, for example,methylbutadiene, dimethylbutadiene and pentadiene as well as copolymerssuch as those formed from butadiene or its homologues or derivativeswith other unsaturated monomers. Among the latter are acetylenes, forexample, vinyl acetylene; olefins, for example, isobutylene, whichcopolymerizes with isoprene to form butyl rubber; vinyl compounds, forexample, acrylic acid, acrylonitrile (which polymerize with butadiene toform NBR), methacrylic acid and styrene, the latter compoundpolymerizing with butadiene to form SBR, as well as vinyl esters andvarious unsaturated aldehydes, ketones and ethers, e.g., acrolein,methyl isopropenyl ketone and vinylethyl ether. Specific examples ofsynthetic rubbers include neoprene (polychloroprene), polybutadiene(including cis-1,4-polybutadiene), polyisoprene (includingcis-1,4-polyisoprene), butyl rubber, halobutyl rubber such aschlorobutyl rubber or bromobutyl rubber, styrene/isoprene/butadienerubber, copolymers of 1,3-butadiene or isoprene with monomers such asstyrene, acrylonitrile and methyl methacrylate, as well asethylene/propylene terpolymers, also known as ethylene/propylene/dienemonomer (EPDM), and in particular, ethylene/propylene/dicyclopentadieneterpolymers. Additional examples of rubbers which may be used includealkoxy-silyl end functionalized solution polymerized polymers (SBR, PBR,IBR and SIBR), silicon-coupled and tin-coupled star-branched polymers.The preferred rubber or elastomers are polyisoprene (natural orsynthetic), polybutadiene and SBR.

In one aspect the at least one additional rubber is preferably of atleast two of diene based rubbers. For example, a combination of two ormore rubbers is preferred such as cis 1,4-polyisoprene rubber (naturalor synthetic, although natural is preferred), 3,4-polyisoprene rubber,styrene/isoprene/butadiene rubber, emulsion and solution polymerizationderived styrene/butadiene rubbers, cis 1,4-polybutadiene rubbers andemulsion polymerization prepared butadiene/acrylonitrile copolymers.

In one aspect of this invention, an emulsion polymerization derivedstyrene/butadiene (E-SBR) might be used having a relatively conventionalstyrene content of about 20 to about 28 percent bound styrene or, forsome applications, an E-SBR having a medium to relatively high boundstyrene content, namely, a bound styrene content of about 30 to about 45percent.

By emulsion polymerization prepared E-SBR, it is meant that styrene and1,3-butadiene are copolymerized as an aqueous emulsion. Such are wellknown to those skilled in such art. The bound styrene content can vary,for example, from about 5 to about 50 percent. In one aspect, the E-SBRmay also contain acrylonitrile to form a terpolymer rubber, as E-SBAR,in amounts, for example, of about 2 to about 30 weight percent boundacrylonitrile in the terpolymer.

Emulsion polymerization prepared styrene/butadiene/acrylonitrilecopolymer rubbers containing about 2 to about 40 weight percent boundacrylonitrile in the copolymer are also contemplated as diene basedrubbers for use in this invention.

The solution polymerization prepared SBR (S-SBR) typically has a boundstyrene content in a range of about 5 to about 50, preferably about 9 toabout 36, percent. The S-SBR can be conveniently prepared, for example,by organo lithium catalyzation in the presence of an organic hydrocarbonsolvent.

In one embodiment, cis 1,4-polybutadiene rubber (BR) may be used. SuchBR can be prepared, for example, by organic solution polymerization of1,3-butadiene. The BR may be conveniently characterized, for example, byhaving at least a 90 percent cis 1,4-content.

The cis 1,4-polyisoprene and cis 1,4-polyisoprene natural rubber arewell known to those having skill in the rubber art.

The term “phr” as used herein, and according to conventional practice,refers to “parts by weight of a respective material per 100 parts byweight of rubber, or elastomer.”

The self-healing rubber composition may also include up to 70 phr ofprocessing oil. Processing oil may be included in the rubber compositionas extending oil typically used to extend elastomers. Processing oil mayalso be included in the rubber composition by addition of the oildirectly during rubber compounding. The processing oil used may includeboth extending oil present in the elastomers, and process oil addedduring compounding. Suitable process oils include various oils as areknown in the art, including aromatic, paraffinic, naphthenic, vegetableoils, and low PCA oils, such as MES, TDAE, SRAE and heavy naphthenicoils. Suitable low PCA oils include those having a polycyclic aromaticcontent of less than 3 percent by weight as determined by the IP346method. Procedures for the IP346 method may be found in Standard Methodsfor Analysis & Testing of Petroleum and Related Products and BritishStandard 2000 Parts, 2003, 62 nd edition, published by the Institute ofPetroleum, United Kingdom.

The self-healing rubber composition may include from about 10 to about150 phr of silica. In another embodiment, from 20 to 80 phr of silicamay be used.

The commonly employed siliceous pigments which may be used in the rubbercompound include conventional pyrogenic and precipitated siliceouspigments (silica). In one embodiment, precipitated silica is used. Theconventional siliceous pigments employed in this invention areprecipitated silicas such as, for example, those obtained by theacidification of a soluble silicate, e.g., sodium silicate. Suchconventional silicas might be characterized, for example, by having aBET surface area, as measured using nitrogen gas. In one embodiment, theBET surface area may be in the range of about 40 to about 600 squaremeters per gram. In another embodiment, the BET surface area may be in arange of about 80 to about 300 square meters per gram. The BET method ofmeasuring surface area is described in the Journal of the AmericanChemical Society, Volume 60, Page 304 (1930).

The conventional silica may also be characterized by having adibutylphthalate (DBP) absorption value in a range of about 100 to about400, alternatively about 150 to about 300.

The conventional silica might be expected to have an average ultimateparticle size, for example, in the range of 0.01 to 0.05 micron asdetermined by the electron microscope, although the silica particles maybe even smaller, or possibly larger, in size.

Various commercially available silicas may be used, such as, only forexample herein, and without limitation, silicas commercially availablefrom PPG Industries under the Hi-Sil trademark with designations 210,243, etc; silicas available from Rhodia, with, for example, designationsof Z1165MP and Z165GR and silicas available from Degussa AG with, forexample, designations VN2 and VN3, etc.

Commonly employed carbon blacks can be used as a conventional filler inan amount ranging from 10 to 150 phr. In another embodiment, from 20 to80 phr of carbon black may be used. Representative examples of suchcarbon blacks include N110, N121, N134, N220, N231, N234, N242, N293,N299, N315, N326, N330, N332, N339, N343, N347, N351, N358, N375, N539,N550, N582, N630, N642, N650, N683, N754, N762, N765, N774, N787, N907,N908, N990 and N991. These carbon blacks have iodine absorptions rangingfrom 9 to 145 g/kg and DBP number ranging from 34 to 150 cm³/100 g.

Other fillers may be used in the self-healing rubber compositionincluding, but not limited to, particulate fillers including ultra highmolecular weight polyethylene (UHMWPE), crosslinked particulate polymergels including but not limited to those disclosed in U.S. Pat. Nos.6,242,534; 6,207,757; 6,133,364; 6,372,857; 5,395,891; or 6,127,488, andplasticized starch composite filler including but not limited to thatdisclosed in U.S. Pat. No. 5,672,639. Such other fillers may be used inan amount ranging from 1 to 30 phr.

In one embodiment the self-healing rubber composition may contain aconventional sulfur containing organosilicon compound. Examples ofsuitable sulfur containing organosilicon compounds are of the formula:

Q-Alk-S_(n)-Alk-Q  V

in which Q is selected from the group consisting of

where R³ is an alkyl group of 1 to 4 carbon atoms, cyclohexyl or phenyl;R⁴ is alkoxy of 1 to 8 carbon atoms, or cycloalkoxy of 5 to 8 carbonatoms; Alk is a divalent hydrocarbon of 1 to 18 carbon atoms and n is aninteger of 2 to 8.

In one embodiment, the sulfur containing organosilicon compounds are the3,3′-bis(trimethoxy or triethoxy silylpropyl)polysulfides. In oneembodiment, the sulfur containing organosilicon compounds are3,3′-bis(triethoxysilylpropyl)disulfide and/or3,3′-bis(triethoxysilylpropyl)tetrasulfide. Therefore, as to formula V,Q may be

where R⁴ is an alkoxy of 2 to 4 carbon atoms, alternatively 2 carbonatoms; alk is a divalent hydrocarbon of 2 to 4 carbon atoms,alternatively with 3 carbon atoms; and n is an integer of from 2 to 5,alternatively 2 or 4.

In another embodiment, suitable sulfur containing organosiliconcompounds include compounds disclosed in U.S. Pat. No. 6,608,125. In oneembodiment, the sulfur containing organosilicon compounds includes3-(octanoylthio)-1-propyltriethoxysilane,CH₃(CH₂)₆C(═O)—S—CH₂CH₂CH₂Si(OCH₂CH₃)₃, which is available commerciallyas NXT™ from Momentive Performance Materials.

In another embodiment, suitable sulfur containing organosiliconcompounds include those disclosed in U.S. Patent Publication No.2003/0130535. In one embodiment, the sulfur containing organosiliconcompound is Si-363 from Degussa.

The amount of the sulfur containing organosilicon compound in a rubbercomposition will vary depending on the level of other additives that areused. Generally speaking, the amount of the compound will range from 0.5to 20 phr. In one embodiment, the amount will range from 1 to 10 phr.

It is readily understood by those having skill in the art that theself-healing rubber composition would be compounded by methods generallyknown in the rubber compounding art, such as mixing the varioussulfur-vulcanizable constituent rubbers with various commonly usedadditive materials such as, for example, sulfur donors, curing aids,such as activators and retarders and processing additives, such as oils,resins including tackifying resins and plasticizers, fillers, pigments,fatty acid, zinc oxide, waxes, antioxidants and antiozonants andpeptizing agents. As known to those skilled in the art, depending on theintended use of the sulfur vulcanizable and sulfur-vulcanized material(rubbers), the additives mentioned above are selected and commonly usedin conventional amounts. Representative examples of sulfur donorsinclude elemental sulfur (free sulfur), an amine disulfide, polymericpolysulfide and sulfur olefin adducts. In one embodiment, thesulfur-vulcanizing agent is elemental sulfur. The sulfur-vulcanizingagent may be used in an amount ranging from 0.5 to 8 phr, alternativelywith a range of from 1.5 to 6 phr. Typical amounts of tackifier resins,if used, comprise about 0.5 to about 10 phr, usually about 1 to about 5phr. Typical amounts of processing aids comprise about 1 to about 50phr. Typical amounts of antioxidants comprise about 1 to about 5 phr.Representative antioxidants may be, for example,diphenyl-p-phenylenediamine and others, such as, for example, thosedisclosed in The Vanderbilt Rubber Handbook (1978), Pages 344 through346. Typical amounts of antiozonants comprise about 1 to 5 phr. Typicalamounts of fatty acids, if used, which can include stearic acid compriseabout 0.5 to about 3 phr. Typical amounts of zinc oxide comprise about0.1 to about 5 phr. Lower amounts of zinc oxide may be used to avoidcomplexation with the functionalized elastomer. Typical amounts of waxescomprise about 1 to about 5 phr. Often microcrystalline waxes are used.Typical amounts of peptizers comprise about 0.1 to about 1 phr. Typicalpeptizers may be, for example, pentachlorothiophenol anddibenzamidodiphenyl disulfide.

Accelerators are used to control the time and/or temperature requiredfor vulcanization and to improve the properties of the vulcanizate. Inone embodiment, a single accelerator system may be used, i.e., primaryaccelerator. The primary accelerator(s) may be used in total amountsranging from about 0.5 to about 4, alternatively about 0.8 to about 1.5,phr. In another embodiment, combinations of a primary and a secondaryaccelerator might be used with the secondary accelerator being used insmaller amounts, such as from about 0.05 to about 3 phr, in order toactivate and to improve the properties of the vulcanizate. Combinationsof these accelerators might be expected to produce a synergistic effecton the final properties and are somewhat better than those produced byuse of either accelerator alone. In addition, delayed actionaccelerators may be used which are not affected by normal processingtemperatures but produce a satisfactory cure at ordinary vulcanizationtemperatures. Vulcanization retarders might also be used. Suitable typesof accelerators that may be used in the present invention are amines,disulfides, guanidines, thioureas, thiazoles, thiurams, sulfenamides,dithiocarbamates and xanthates. In one embodiment, the primaryaccelerator is a sulfenamide. If a second accelerator is used, thesecondary accelerator may be a guanidine, dithiocarbamate or thiuramcompound.

The mixing of the self-healing rubber composition can be accomplished bymethods known to those having skill in the rubber mixing art. Forexample, the ingredients are typically mixed in at least two stages,namely, at least one non-productive stage followed by a productive mixstage. The final curatives including sulfur-vulcanizing agents aretypically mixed in the final stage which is conventionally called the“productive” mix stage in which the mixing typically occurs at atemperature, or ultimate temperature, lower than the mix temperature(s)than the preceding non-productive mix stage(s). The terms“non-productive” and “productive” mix stages are well known to thosehaving skill in the rubber mixing art. The rubber composition may besubjected to a thermomechanical mixing step. The thermomechanical mixingstep generally comprises a mechanical working in a mixer or extruder fora period of time suitable in order to produce a rubber temperaturebetween 140° C. and 190° C. The appropriate duration of thethermomechanical working varies as a function of the operatingconditions, and the volume and nature of the components. For example,the thermomechanical working may be from 1 to 20 minutes.

The self-healing rubber composition may be incorporated in a variety ofrubber components of the tire as are known in the art. For example, therubber component may be a tread (including tread cap and tread base),sidewall, apex, chafer, sidewall insert, wirecoat or innerliner.

The pneumatic tire of the present invention may be a race tire,passenger tire, aircraft tire, agricultural, earthmover, off-the-road,truck tire, and the like. In one embodiment, the tire is a passenger ortruck tire. The tire may also be a radial or bias.

Vulcanization of the pneumatic tire of the present invention isgenerally carried out at conventional temperatures ranging from about100° C. to 200° C. In one embodiment, the vulcanization is conducted attemperatures ranging from about 110° C. to 180° C. Any of the usualvulcanization processes may be used such as heating in a press or mold,heating with superheated steam or hot air. Such tires can be built,shaped, molded and cured by various methods which are known and will bereadily apparent to those having skill in such art.

While the invention as described herein has been directed to tires, themethod is not so limited. Other applications of the self healing rubbercomposition can be envisioned. Any rubber or elastomer article ofmanufacture can utilize the self healing rubber composition as describedherein. For example, applications of the self healing rubber compositiondescribed herein include hoses, transmission belts, drive belts, airsprings, conveyor belts, drive tracks, shoe soles and the like.

The invention is further illustrated by the following non-limitingexamples.

Example 1

In this example, functionalization of a styrene-butadiene rubber with2-mercaptonaphthalene is illustrated to demonstrate the thiol-enereaction.

To test the reactivity and reaction conditions of the styrene-butadienerubber in a thiol-ene reaction, some reactions with a model thiol weremade. The chosen thiol was 2-mercaptonaphthalene, from Aldrich.

The properties of the used styrene-butadiene rubber are summarized inTable 1. FIG. 4 shows the ¹H-NMR spectrum of the elastomer.

TABLE 1 Mooney (avg) 27.6 Finished Mooney 23.1 Tg (onset)/° C. −21.74 Tg(midpoint)/° C. −17.52 FTIR Styrene 25.392 FTIR Vinyl 47.506 FTIR Cis13.144 FTIR Trans 13.058 Mn/g/mol 124122 Mw/g/mol 207982 Mz/g/mol 327454PDI 1.67

Synthesis of 2-mercaptonaphthalene Functionalized Rubber

This compound was synthesized twice, once with AIBN as initiator for thereaction and once with an acylphosphine oxide photoinitiator (LucirinTPO).

For the reaction initiated by AIBN, 1 g of SBR was dissolved in 50 mldry THF and 1.40 g of 2-mercaptonaphthalene and 0.14 g AIBN were added.The solution was degassed under a stream of argon for 2 hours and wasthen placed in a preheated oil bath at 75° C. The reaction was stirredfor 14.5 hours at that temperature.

For the reaction initiated by the photoinitiator, a mixture of 1 g SBR,1.40 g 2-mercaptonaphthalene and 0.30 g Lucirin TPO was degassed under astream of argon for 2 hours and then was placed under a UV-lamp (320-380nm) for 14.5 hours.

To make sure that no free thiol was present in the product, bothreaction mixtures were dialyzed against THF for two days. Afterwards thesolvent was evaporated and the product was dried under vacuum.

FIG. 5 shows the UV-vis spectrum of the elastomer before (1) and afterthe reaction with 2-mercaptonaphtalene (2) and the spectrum of the purethiol (3). Here the photoinitiator was used. FIG. 6 shows the same forthe reaction which was initiated by AIBN, with the UV-vis spectrum ofthe elastomer before (1) and after the reaction with2-mercaptonaphthanline (2) and the spectrum of the pure thiol (3).

FIG. 7 shows the ¹H-NMR spectrum of the elastomer before (1) and afterreaction with the thiol in the presence of AIBN (2) and Lucirin (3).Compared to the ¹H-NMR spectrum of the unfunctionalized rubber, there isan increase of the signals for the aromatic protons and a decrease forthe vinyl groups after the polymer analogous reaction, confirming thatthe SBR was successfully functionalized with 2-mercaptonaphthalene.GPC-measurement (in THF) as shown in FIG. 8 for the SBR (1), the SBRfunctionalized in the presence of AIBN (2) and in the presence ofLucirin (3) confirmed that the product is not greatly cross linked. Asseen in FIG. 8, especially the curve of the AIBN-initiated product (2)shows very little cross linking (small shoulder), so that the decreaseof the signal of vinyl protons can be assigned to functionalization.

Example 2

In this example, functionalization of a styrene-butadiene rubber with6-(2,2′;6′,2″-terpyridin-4′-ylsulfanyl)hexane-1-thiole (formula VI) isillustrated.

Synthesis of 6-(2,2′;6′,2″-terpyridin-4′-ylsulfanyl)hexane-1-thiol

The terpyridine of formula VI was obtained in a 4 step reaction usingliterature procedures [U. S. Schubert, C. Eschbaumer, O. Hien, P. R.Andres, Tetrahedron Lett. 2001, 42, 4705; U. S. Schubert, S. Schmatloch,A. A. Precup, Designed Monomers and Polymers 2002, 5, 211.]. The yieldand analysis at each step was as follows:

Step 1: 1,5-bis-(2′-pyridyl)-1,3,5-tricarbonyl pentane

Ethylpicolinate was reacted with acetone in the presence of NaH intetrahydrofuran. The reaction mixture was refluxed for eight hours.Yield: 41% yellow crystals

¹H-NMR (CDCl₃/300 MHz): δ[ppm]: 2.10 (s, 4H); 7.24 (s, CDCl3); 7.40-7.44(m, 2H); 7.84-7.95 (m, 4H); 8.76-8.77 (m, 2H)

Step 2: 2,6-bis-(2′-pyridyl)-4-pyridone

The product of step 1 was reacted with ammonium acetate with a 48 hourreflux. Yield: 67% light pink crystals

¹H-NMR (CDCl₃/300 MHz): δ[ppm]: 6.77 (s, 2H); 7.24 (s, CDCl3); 7.36-7.38(m, 2H); 7.77-7.86 (m, 4H); 8.64-8.66 (m, 2H)

Step 3: 4′-chloro-2,2′;6′,2″-terpyridine

The product of step 2 was reacted with potassium pentachloride inphosphoryl chloride with a 24 hour reflux.

Yield: 55% light purple

¹H-NMR (CDCl₃/300 MHz): δ[ppm]: 7.24 (s, CDCl3); 7.80-7.86 (m, 2H); 8.46(s, 2H); 8.55 (t, 2H); 8.58 (t, 2H); 8.66-8.69 (m, 2H)

Step 4: 6-(2,2′;6′,2″-terpyridin-4′-ylsulfanyl)hexane-1-thiol

The product of step 3 was reacted with 1,6-hexanedithiol in the presenceof potassium hydroxide in dimethylsulfoxide.

Yield: 35% colorless crystals

¹H-NMR (CDCl₃/300 MHz): δ[ppm]: 1.32-1.63 (m, 4H), 1.79-1.88 (m, 4H),3.63 (q, 2H), 4.7 (t, 2H), 7.24 (s, CDCl3); 7.27-7.32 (m, 2H); 7.78-7.84(m, 2H); 7.96 (s, 2H); 8.56-8.65 (m, 4H)

The styrene butadiene rubber of Example 1 was functionalized with6-(2,2;6′,2″-terpyridin-4′-ylsulfanyl)hexane-1-thiol following theprocedures of Example 1 for 2-mercaptonaphthalene.

FIG. 9 shows the ¹H-NMR of the unfunctionalized elastomer (1) comparedto the rubber functionalized with the terpyridine ligand (2), and theterpyridine (3). As seen in FIG. 9, a small amount of the ligand hasreacted with the vinylgroups of the elastomer. Very small signals in thearomatic region of the functionalized rubber spectrum (2) between 8 and9 ppm belonging to the hydrogen of the ligand can be observed,indicating a successful functionalization. FIG. 10 shows a GPC graph forthe SBR (1) and the functionalized SBR (2). As seen in FIG. 10,essentially no change in molecular weight could be observed in the GPCmeasurement, so that the reduction of vinylprotons can be assigned tofunctionalization.

Example 3

In this example, functionalization of a styrene-butadiene rubber with4′-mercapto-2,2′:6′,2″-terpyridine (formula VII) is illustrated

Synthesis of -4′-mercapto-2,2′:6′,2″-terpyridine

The terpyridine of formula VII was obtained using the 4 step procedureas given in Example 2, with the modification that in step 4, the4′-chloro-2,2′;6′,2″-terpyridine product of step 3 was reacted withsodium hydrogensulfide (NaSH) in the presence of potassium hydroxide indimethylformamide (DMF).

Yield: 88%

The styrene butadiene rubber of Example 1 was functionalized with4′-mercapto-2,2′:6′,2″-terpyridine following the procedures of Example 1for 2-mercaptonaphthalene.

FIG. 11 shows the ¹H-NMR of the unfunctionalized elastomer (1) comparedto the rubber functionalized with the terpyridine ligand (2). As seen inFIG. 11, a small amount of the ligand has reacted with the vinylgroupsof the elastomer. Very small signals in the aromatic region of thefunctionalized rubber spectrum (2) between 8 and 9 ppm belonging to thehydrogen of the ligand can be observed, indicating a successfulfunctionalization.

Example 4

In this example, functionalization of a styrene-butadiene rubber with4′-(4-mercaptomethylphenyl)-2,2′:6,2″-terpyridine (formula VIII) isillustrated.

Synthesis of 4′-(4-mercaptomethylphenyl)-2,2′:6,2″-terpyridine

The terpyridine of formula VIII was obtained following a synthesis routeas shown in FIG. 12.

Step 1: 4′-methylphenyl-2,2′:6,2″-terpyridine

-   [X. J. Zhang, D. Li, X. P. Zhou, New J. Chem. 2006, 30, 706.]

4.6 g (0.115 mol) NaOH was mixed with 6.4 g (0.05 mol) p-tolylaldehydeand 12.8 g (0.10 mol) 2-acetylpyridine in a mortar, until a yellowpowder was produced. The powder was transferred to a flask whichcontained 35 g ammonia acetate (excess) and 90 ml acetic acid (100%).The mixture was heated under reflux for three hours. Afterwards 50 mlethanol and 68 ml water were added. Upon cooling the red solution theproduct crystallized. It was recrystallized from ethanol twice.

Yield: 65% light yellow crystals

¹H-NMR (CDCl₃/300 MHz): δ[ppm]: 2.41 (s, 3H); 7.29-7.37 (m, 4H); 7.81(d, 2H); 7.87 (td, 2H); 8.66 (d, 2H); 8.71-8.73 (m, 4H)

Step 2: 4′-(4-bromomethylphenyl)-2,2′:6,2″-terpyridine

7.07 g 4′-methylphenyl-2,2′:6,2″-terpyridine, 0.28 g AIBN and 4.67 gN-Bromsuccinimide were dissolved in 70 ml benzene and heated under refuxfor 6 hours.

The resulting suspension was filtered hot to remove the succinimide. Thesolvent of the filtrate was evaporated and the resulting solid wasrecrystallized from ethanol/aceton 2:1.

Yield: 60% dark yellow crystals

¹H-NMR (CDCl₃/300 MHz): δ[ppm]: 4.55 (s, 2H); 7.33-7.38 (m, 2H); 7.52(d, 2H); 7.85-7.92 (m, 4H); 8.66 (td, 2H); 8.71-8.73 (m, 4H)

Step 3: 4′-(4-isothiouroniumbromidemethylphenyl)-2,2′:6,2″-terpyridine

This step was carried out according to the literature procedure [G. C.Zhou, Harruna, II, Macromolecules 2005, 38, 4114].

Yield: 75%

Step 4: 4′-(4-mercaptomethylphenyl)-2,2′:6,2″-terpyridine

This step was carried out according to the literature procedure [G. C.Zhou, Harruna, II, Macromolecules 2005, 38, 4114].

Yield: 95%

¹H-NMR (CDCl₃/300 MHz): δ[ppm]: 3.69 (s, 2H); 7.28-7.38 (m, 4H);7.81-7.88 (m, 4H); 8.61-8.70 (m, 6H)

The styrene butadiene rubber of Example 1 was functionalized with4:4′-(4-mercaptomethylphenyl)-2,2′:6,2″-terpyridine following theprocedures of Example 1 for 2-mercaptonaphthalene.

FIG. 13 shows the ¹H-NMR of the rubber functionalized with theterpyridine ligand (2), and the terpyridine (1). As seen in FIG. 13, asmall amount of the ligand has reacted with the vinylgroups of theelastomer. Very small signals in the aromatic region of thefunctionalized rubber spectrum (2) between 8 and 9 ppm belonging to thehydrogen of the ligand can be observed, indicating a successfulfunctionalization.

Example 5

In this example, the effect of adding a iron salt to a functionalizedelastomer is illustrated. A rubber cement was prepared by adding 0.4 gof the functionalized elastomer of Example 4 to 4 ml of THF in a smallvial. The rubber cement was combined with 0.02 g of FeSO₄.7H₂O and thevial was shaken for 7 hours. Visual inspection of the rubbercement/metal salt mixture showed a purple color, as compared with thecolorless rubber cement.

UV-vis spectra for the rubber cement/metal salt and rubber cement areshown in FIG. 14. As seen in FIG. 14, the rubber cement/metal saltspectrum (2) shows an absorbance peak at about 571 nm, indicating theformation of a coordination complex between the terpyridine moieties ofthe functionalized elastomer and the Fe²⁺ ion. The rubber cementspectrum (1) shows no such peak.

Example 6

In this example, the effect of adding a ruthenium salt to afunctionalized elastomer is illustrated. A rubber cement was prepared byadding 0.03 g of the functionalized elastomer of Example 4 to 5 ml THFand 0.25 ml MeOH in a small vial. The rubber cement was combined with0.02 g of RuCl₃ and the vial was heated up to 65° C. for 20 hours andshaken. Visual inspection of the rubber cement/metal salt mixture showeda dark red color, as compared with the colorless rubber cement.

UV-vis spectra for the rubber cement/metal salt and rubber cement areshown in FIG. 15. As seen in FIG. 15, the rubber cement/metal saltspectrum (2) shows an absorbance peak at about 490 nm, indicating theformation of a coordination complex between the terpyridine moieties ofthe functionalized elastomer and the Ru²⁺ ion. The rubber cementspectrum (1) shows no such peak.

What is claimed is:
 1. A self-healing rubber composition comprising afunctionalized elastomer comprising: a polymeric backbone chain derivedfrom a monomer comprising at least one conjugated diene monomer andoptionally at least one vinyl aromatic monomer; and a functional groupbonded to the backbone chain, the functional group comprising amultidentate ligand capable of complexing with a metal ion; and apartitioned metal ion.
 2. A self-healing rubber composition comprising afunctionalized diene-based elastomer of formula IXY—Z]_(n)  (I) wherein X is a polymer derived from a monomer comprisingat least one conjugated diene monomer and optionally at least one vinylaromatic monomer, Z comprises a multidentate ligand group capable ofcomplexing with a metal ion, Y is a divalent group bonded to both X andZ, n is the number of Y—Z] groups bonded to X; and a partitioned metalion.
 3. The self-healing rubber composition of claim 2, wherein Zcomprises a ligand selected from the group consisting of a substitutedbipyridinyl groups, unsubstituted bipyridinyl groups, substitutedterpyridinyl groups, unsubstituted terpyridinyl groups, substitutedphenanthrolinyl groups, unsubstituted phenanthrolinyl groups,substituted pyrazinyl groups, and unsubstituted pyrazinyl groups.
 4. Theself-healing rubber composition of claim 2, wherein Z comprises a ligandof formula II, II or IV

where R¹ forms the linkage from Z to Y in formula I and R¹ is a covalentbond, C2 to C8 linear alkylene, arylene, alkyl substituted arylene, arylsubstituted alkylene, thioalkylene, or thioarylene, and R² areindependently selected from the group consisting of hydrogen, C2 to C6linear alkyl, and C2 to C6 branched alkyl.
 5. The self-healing rubbercomposition of claim 2, where Y is divalent sulfur.
 6. The self-healingrubber composition of claim 2, wherein Z comprises a ligand selectedfrom the group consisting of substituted 2,2′;6′2″-terpyridinyl groups,unsubstituted 2,2′;6′2″-terpyridinyl groups, substituted2,2′-bipyridinyl groups, and unsubstituted 2,2′-bipyridinyl groups. 7.The self-healing rubber composition of claim 2, wherein Y—Z] group isselected from the group consisting of6-(2,2′;6′,2″-terpyridin-4′-ylsulfanyl)hexyl-1-sulfanyl,2,2′;6′,2″-terpyridin-4′-ylsulfanyl, and4-(2,2′;6′,2″-terpyridin-4′-yl)phenylmethylsulfanyl.
 8. The self-healingrubber composition of claim 2, wherein X is selected from the groupconsisting of styrene-butadiene rubbers, polybutadiene rubbers, andpolyisoprene rubbers.
 9. The self-healing rubber composition of claim 2,wherein n ranges from 2 to
 30. 10. The self-healing rubber compositionof claim 2, wherein the metal ion comprises a metal salt.
 11. Theself-healing rubber composition of claim 2, wherein the metal ioncomprises a metal nanoparticle.
 12. The self-healing rubber compositionof claim 2, wherein the metal ion is selected from the group consistingof Cu²⁺, Fe²⁺, Co²⁺, Ni²⁺, Zn²⁺ and Ru²⁺.
 13. The self-healing rubbercomposition of claim 2, wherein the partitioned metal ion comprises amechanically disruptible partition.
 14. The self-healing rubbercomposition of claim 2, wherein the partitioned metal ion comprises anencapsulated metal ion.
 15. The self-healing rubber composition of claim2, wherein the partitioned metal ion comprises an encapsulated metalion, and the encapsulated metal ion comprises a metal salt encapsulatedby a coating material selected from the group consisting ofpolyurethanes, gelatins, polyureas, polystyrenes, polydivinylbenzenes,and polyamides.
 16. The self-healing rubber composition of claim 2,wherein the encapsulated metal ion is coated with an adhesive.
 17. Theself-healing rubber composition of claim 2, wherein the partitionedmetal ion comprises a polymeric ligand.
 18. The self healing rubbercomposition of claim 12, wherein the partitioned metal ion comprises apolymeric ligand selected from the group consisting of polyamines andpolycarboxylic acids.
 19. A pneumatic tire comprising the rubbercomposition of claim
 2. 20. An article of manufacture comprising therubber composition of claim 2, wherein the article of manufacture isselected from the group consisting of hoses, transmission belts, drivebelts, air springs, conveyor belts, drive tracks, and shoe soles.